1. Technical Field
The present embodiment relates to a rubber composition and a pneumatic tire using the rubber composition.
2. Related Art
A tire is required to have excellent grip performance on a wet road surface (wet performance). On the other hand, in recent tires, the requirement to low fuel consumption is high, and excellent rolling resistance performance, that is, low rolling resistance, is required. However, those performances are conflicting characteristics, and are generally difficult to achieve simultaneously.
JP-A-02-114003 discloses a blend of cis-1,4-polyisoprene rubber and isoprene-acrylonitrile rubber or butadiene-acrylonitrile rubber in order to obtain a tread having balanced viscoelasticity relating to wet performance and rolling resistance performance. JP-A-2000-302915 discloses a rubber composition in which to obtain a tread rubber having high hysteresis loss and excellent abrasion resistance, other diene rubber is added to acrylonitrile-butadiene rubber (NBR) in a carbon black formulation so that carbon black is not incorporated into an NBR phase. Those patent documents disclose a blend of NBR and other diene rubber, but do not disclose using hydrogenated rubber as NBR.
JP-A-2010-043166 discloses that to achieve high abrasion resistance without deteriorating rolling resistance, carboxyl-modified acrylonitrile-butadiene rubber (NBR) is added to a silica formulation, and discloses that a hydrogenated rubber may be used as the carboxyl-modified NBR. However, this patent document uses NBR modified with a carboxyl group having an interaction with silica for the purpose of incorporating silica into NBR, and does not disclose using a rubber obtained by hydrogenating non-modified NBR.
On the other hand, WO2005/005546 discloses that a polar polymer is added to a rubber component such as natural rubber in order to improve bloom resistance of a crosslinking agent, and discloses that hydrogenated nitrile rubber (HNBR) is used as the polar polymer. However, this patent document does not disclose that modified styrene-butadiene rubber having an interaction with silica is used as a rubber component to be combined with hydrogenated nitrile rubber.
JP-A-2013-010967 discloses that a crosslinkable polymer and three-dimensionally crosslinked fine particles are added to a rubber composition containing a diene rubber and carbon black and/or silica in order to improve on-ice performance and abrasion resistance. This patent document further describes that a rubber modified with an amino group, an alkoxyl group or the like may be used as the diene rubber, and fine particles obtained by three-dimensionally crosslinking a saturated hydrocarbon polymer or copolymer such as hydrogenated nitrile rubber may be used as the fine particles. However, the polymer that forms the fine particles is required to have a reactive functional group such as a hydroxyl group or a silane functional group in order to three-dimensionally crosslink the polymer. From the standpoint of this, it does not say that this patent document discloses adding non-modified hydrogenated NBR to a rubber composition, and this patent document does not suggest the advantageous effects by the combination with modified styrene-butadiene rubber.